Despite his complaint that a new block of flats would overlook his property and have a "negative effect on the appearance of the street," the local council has given the go-ahead for the development next door to the steel billionaire's mansion at the Bishops Avenue in north London.
His £9 million property called the 'Summer Palace' has 11 bedrooms, 13 bathrooms, a gym and a heart-shaped swimming pool and a brass and glass lift.
The neighbour in question is Princess Samerah bin Mokhtar al-Saaddawy of the Saudi Arabian royal family, and the property she is planning to knock down in favour of the flats is "barely more appealing", the Daily Telegraph reported.
An extension to her house began in the mid-1980s but construction stopped a few years later and it has remained semi-derelict.
The Princess has won the approval for two buildings on the site of three and four storeys, linked at basement level, with car parking and a swimming pool underneath and a ballroom at the back. There will be 12 exclusive apartments with balconies.
In an objection lodged on the Mittals' behalf by the consultants Macfarlanes, they claim the property does not represent "high-quality design" and fails to "preserve or enhance local character."
They object to replacing a detached house with flats and add that "neither the height nor the appearance of the new buildings will be compatible with the special character of The Bishops Avenue and they will have a significant adverse visual impact."
Furthermore, there will be a large number of new windows which would "severely reduce" their privacy.
Another neighbour, the tea entrepreneur N K Sethia said, the development would turn the street into a "concrete jungle," ruining its "tidy and serene" atmosphere by allowing "what amounts to a block of flats".
The new block of flats, however, received a glowing appraisal from council planners who pointed out that it had "an architectural approach" which was "evolving, post-modern neo-Jacobean" and "of considerable interest".
"The development," they said, "has been conceived as an English country manor, set upon a terrace with the surrounding outhouses, which refer to barns, stables and agricultural buildings in more vernacular style, which contrast with the main house."
Mittal and Princess al-Saadawy were unavailable for comments.