The terminal, which at the time many observers felt took airport design to new heights and breathed fresh life into Heathrow, was offically opened by the royal couple on April 1.
It cost around £200 million to build and was originally the base for British Airways before they moved to Terminal 5 in 2008.
Terminal 4 welcomed its first passengers on Saturday 12th April 1986, and I, with the rest of Heathrow's then resident press, was there to meet them!
The terminal was upgraded in 2008 and now at 105,481 square metres in size, it houses 35 airlines and serves as the base for the Sky Team airline alliance.
Last year Terminal 4 had 53,357 flights and saw 9.2 million passengers pass through its doors.
Ray Stanley from Woking started working at Heathrow before Terminal 4 was built and has been part of the team there since it opened, claims that his colleagues used to call it "fantasy island" because of its then remote location at the UK gateway.
It has, of course, since been joined by other developments and the even more remote Terminal 5.
Stanley remarks: "There are not many jobs like this where you get to meet such a diverse range of people and have to deal with a variety of issues on a day to day basis.
"I have made some fantastic friends here and when you look at how Heathrow has developed over the years into the airport that it is today, I am very proud to have been part of it.”
Terminal 4 is not the only significant airport milestone this year, with it also being Heathrow’s 70th anniversary.
On 1st January 1946 ownership of Heathrow was transferred to the Ministry of Civil Aviation before handling its first civilian flights in May.
Heathrow intends celebrating the milestone in May.