I am new to automata and learning to make regular expression for languages. But I have been stuck on this one.

Suppose we have a language L, Language of all strings that has exactly 1 triple **“b”** defined over alphabet set **Σ = {a, b}**  

Now after several tries, I came up with this
**(a\* (ab)\* (ba)\* )\* bbb (a\* (ab)\* (ba)\* )\*** but then I realize that this is wrong too because the string **abbbabababb** doesn't fit on this.

Kindly someone point out at my mistake or help me solve it as I have spent almost an hour on this.