When to inform line manager about intending to change role?

Question

I work in the same company since 10 years now, last 5 years in the same position with the same line manager.

I still more or less like what I do and feel well with my manager too.
My communication to him is always that I still like my job, happy to stay there for a few more years and not actively looking for another role.

However from time to time I get offers. So far all was only early information and nothing happened, but sooner or later I'll get one offer interesting enough to change.

I had a call today from a colleague leaving from another department, asking whether she can suggest me as her replacement, and I happily told yes, as I'd like that role.
She knows she'll leave, but it's not yet officially announced (will take several weeks) and before that announcement recruiting process won't start, so I still have a lot of time before anything happens.

When should I inform my line managers about the offer? What should I disclose?

• From one side I feel it would be fair to inform I'm interested in change. Maybe just mentioning I'm not anymore fully committed to stay in the same position for a long time?
  (what if he learns that I'm discussing about new offers? It's not a real risk now, but could happen for offers coming from the same department)
• From the other side I feel it would cause (unnecessary) stress and make our relationship worse for no benefit.

Answer 1

Probably best to wait till the recruiting process begins, unless your colleague suggesting you means you get the job. Otherwise you don't know if you'll get the job yet, you cannot be certain.

Once the recruiting begins maybe mention to your manager you're intending on going for that role. As it progresses just update your boss on the progress that you have made on the recruitment process.